U.S. patent application number 10/169783 was filed with the patent office on 2003-01-02 for device for evaluating a position of balance for the human body.
Invention is credited to Berthonnaud, Eric, Dimnet, Joannes, Roussouly, Pierre.
Application Number | 20030004438 10/169783 |
Document ID | / |
Family ID | 8845950 |
Filed Date | 2003-01-02 |
United States Patent
Application |
20030004438 |
Kind Code |
A1 |
Berthonnaud, Eric ; et
al. |
January 2, 2003 |
Device for evaluating a position of balance for the human body
Abstract
According to the invention, the patient (4) is placed upon a
patient support (3) between an X-ray source (1) and a support for
the target plate (2) sensitive to the X-rays. The patient support
(3) is connected to a device for detecting the horizontal position
of the global axis of gravity (5) of the patient when the X-ray
source (1) is in operation. The patient (4) can, for example,
remain standing. The inventive device can superimpose an image (Hg)
of the global axis of gravity (5) on the digital radiographic image
of the patient (4).
Inventors: |
Berthonnaud, Eric;
(Charbonnieres Les Bains, FR) ; Dimnet, Joannes;
(Caluire Et Cuire, FR) ; Roussouly, Pierre; (Saint
Cyr Au Mont D'Or, FR) |
Correspondence
Address: |
William H Eilberg
420 Old York Road
Jenkintown
PA
19046
US
|
Family ID: |
8845950 |
Appl. No.: |
10/169783 |
Filed: |
July 3, 2002 |
PCT Filed: |
January 10, 2001 |
PCT NO: |
PCT/FR01/00060 |
Current U.S.
Class: |
600/595 |
Current CPC
Class: |
A61B 6/505 20130101;
A61B 6/0487 20200801; A61B 6/04 20130101; A61B 5/4023 20130101 |
Class at
Publication: |
600/595 |
International
Class: |
A61B 005/103 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 1, 2000 |
FR |
00 00497 |
Claims
1. A system for evaluating an equilibrium position of the human
body, including a source (1) of X-rays, means for supporting a
target plate (2) sensitive to X-rays to produce on the target plate
(2) a radiographic image of the patient, and patient support means
(3) for supporting a patient (4) in a fixed position between the
source (1) of X-rays and the support means for the target plate (2)
and for generating position signals imaging the horizontal position
of the global axis of gravity (5) of the patient (4) relative to
the source (1) of X-rays and the target plate (2), characterized in
that it includes: scanning means (20) for digitizing the
radiographic image of the patient produced on the target plate (2),
and thereby generating a digitized radiographic image, means (21)
for generating, as a function of said position signals, a digitized
image of the cast shadow (Hg) of the global axis of gravity (5) in
the plane of the target plate (2), means (21) for combining with
said digitized radiographic image of the patient the digitized
image (Hg) of the cast shadow of the global axis of gravity (5),
and thereby generating a combined digitized image, and means (23)
for viewing said combined digitized image.
2. A system according to claim 1, characterized in that the means
for generating a digitized image of the cast shadow of the global
axis of gravity include: a calculation unit (21) and an associated
memory (24) in which geometrical data are stored corresponding to
the relative positions of the source (1) of X-rays, the plane of
the sensitive plate (2), and the patient support means (3) in a
fixed system of axes (XbObYb), a program stored in a program memory
area (26) of the memory (24), adapted for storing said position
signals at the time of taking the radiographic image, calculating,
as a function of said position signals, the straight line segment
(Hg) intersecting the plane of the sensitive plate (2) and the
vertical plane passing through the source (1) of X-rays and the
horizontal position (Og) of the global axis of gravity (5), and
storing the result of this calculation, which constitutes the image
of the global axis of gravity.
3. A system according to claim 2, characterized in that: it
includes a scanner (20) for scanning the radiographic image
produced on the target plate (2) sensitive to X-rays and producing
a series of digital signals constituting the digitized radiographic
image, the program is adapted to receive said digital signals and
stores them in the memory (24), the program is adapted to modify
the stored digitized radiographic image by substituting the image
of the global axis of gravity (Hg), thereby generating said
combined digitized image, and the program is adapted to display
said combined digitized image on a monitor (23), or prints it out
on a support.
4. A system according to either claim 2 or claim 3, characterized
in that the program includes a calibration sequence, adapted for
scanning the radiographic image of a calibration object (40) with
radio-opaque markers (A, B, C, D, E, F, G, H), and for calculating
said geometrical data from known positions and dimensions of the
radio-opaque markers of said calibration object (40), and storing
the data in the memory (24).
5. A system according to any of claims 2 to 4, characterized in
that it includes: patient support means (3) having a modified
weighing machine force plate (15) carried by a plurality of sensors
(C1, C2, C3) arranged at marked positions relative to the system of
axes (XbObYb) and producing force signals used by the calculation
unit and the program as position signals, a removable calibration
weight which can be positioned on the patient support means (3),
has a particular shape, has position marker means which can be made
to coincide with complementary marker means on the patient support
means (3), and has a center of gravity whose position relative to
the position marker means is known, the stored program including a
calibration sequence calculates correction parameters for force
signals produced by each sensor (C1, C2, C3) to make the calculated
center of gravity coincide with the known geometrical position of
the real center of gravity of the calibration weight, which
correction parameters are then stored in memory for subsequent
reliable calculation of the position of the global axis of gravity
of patients.
6. A system according to any of claims 2 to 5, characterized in
that said fixed system of axes (XbObYb) has its center (Ob) in the
vertical plane (XOZ) passing through the source (1) of X-rays and
perpendicular to the support means for the target plate (2)
sensitive to X-rays.
7. A system according to any of claims 2 to 6, characterized in
that it is adapted to take a radiographic image of the thoracic
area, the lumbar area, the pelvic area and the upper femoral area
of the patient (4).
8. A system according to any of claims 2 to 7, characterized in
that the patient support means (3) are rotatable about a median
vertical axis (10) to orient the patient (4) angularly relative to
the direction of propagation of rays between the source (1) of
X-rays and the support means for the target plate (2).
9. A system according to claim 8, characterized in that the patient
support means (3) include armrests (8, 9) on which the patient (4)
can rest his arms (6, 7) in a defined advanced position.
10. The system according to claim 9, characterized in that the
armrests (8, 9) are attached to a turntable (13) which carries a
modified weighing machine force plate (15) on a plurality of force
sensors (C1, C2, C3) distributed at marked positions relative to
the system of axes (XbObYb) and producing force signals used as
position signals by the calculation unit and the program.
11. A system according to any of claims 8 to 10, characterized in
that it includes means for indexing the angular position of the
patient support means (3) at least every 45.degree..
Description
TECHNICAL FIELD OF THE INVENTION
[0001] The present invention concerns a device for evaluating an
equilibrium position of the human body, in particular an
equilibrium position of the spinal column.
[0002] The diagnosis of back pain is generally based on
interpreting one or more radiographic images, produced by a machine
including a source of X-rays, support means for a target plate
sensitive to X-rays, and patient support means adapted to support a
patient in a fixed position between the source of X-rays and the
target plate support means. The practitioner must interpret the
radiographic images to deduce therefrom the probable causes of the
patient's back pain.
[0003] Analyzing radiographic images is difficult, and despite the
great experience of practitioners, this analysis does not take
sufficiently reliable and complete account of the causes of some
spinal afflictions. In some cases, the radiographic images lead to
diagnostic errors.
[0004] To effect a more comprehensive analysis of the human
skeleton, with the aim of understanding better the origin of some
back pains afflicting patients, the documents NL 7 415 910 A and EP
0 119 660 A have already proposed marking the vertical axis passing
through the center of gravity of the patient automatically on a
radiographic image of the spinal column. To this end a system
described in these documents includes a source of X-rays, means for
supporting a target plate sensitive to X-rays, patient support
means adapted to support a patient in a fixed position between the
source of X-rays and the target plate support means, and means
associated with the patient support means to detect the horizontal
position of the global axis of gravity of the patient during
operation of the source of X-rays and to generate position signals.
The position signals control a top carriage moving transversely and
supporting a vertical plumbline placed between the patient and the
support for the target plate sensitive to X-rays, with the aim of
aligning the plumbline with the source of X-rays and the global
axis of gravity. In this way the position of the global axis of
gravity of the patient can be seen in the radiographic image,
characterizing the equilibrium of the patient.
[0005] The above kind of device nevertheless has a number of
drawbacks that prevent its effective use in practice. First of all,
the precision and reliability of the position of the global axis of
gravity in the radiographic image are unsatisfactory. Most
importantly, the mechanical system with a mobile carriage and a
vertical plumbline is a nuisance and a source of errors because of
its bulkiness, the risks of the plumbline snagging, and the
attention that must necessarily be paid to the time of movement of
the plumbline support carriage.
[0006] Another drawback results generally from the variable and
uncontrolled position of the patient on the patient support means,
which degrades the readability of the radiographic image.
SUMMARY OF THE INVENTION
[0007] The problem addressed by the present invention is that of
designing a new system avoiding the drawbacks of prior art systems,
in particular by eliminating all sources of nuisance and errors
that can stem from the use of a mobile vertical plumbline, and by
making totally transparent to the user the transfer of the position
of the global axis of gravity of the patient onto the radiographic
image.
[0008] Another problem addressed by the invention is that of
improving the accuracy and reliability of the radiographic images
obtained in this way, to enable high-resolution interpretation of
the position of the global axis of gravity relative to the skeleton
of the patient.
[0009] To achieve the above and other objects, the invention
provides a system for evaluating an equilibrium position of the
human body, including a source of X-rays and means for supporting a
target plate sensitive to X-rays to produce on the target plate a
radiographic image of the patient, and patient support means for
supporting a patient in a fixed position between the source of
X-rays and the support means for the target plate and for
generating position signals imaging the horizontal position of the
global axis of gravity of the patient relative to the source of
X-rays and the target plate;
[0010] The system according to the invention includes:
[0011] scanning means for digitizing the radiographic image of the
patient produced on the target plate, and thereby generating a
digitized image,
[0012] means for generating, as a function of said position
signals, a digitized image of the cast shadow of the global axis of
gravity in the plane of the target plate,
[0013] means for combining with said digitized radiographic image
of the patient the digitized image of the cast shadow of the global
axis of gravity, and thereby generating a combined digitized
image,
[0014] and means for viewing said combined digitized image.
[0015] The image is therefore produced by electronic means situated
entirely outside the space occupied by the patient when taking the
radiographic image, and totally insensitive to the risks of being
displaced by movements of the patient. Moreover, the accuracy of
the image obtained in this way is significantly improved, since
plumbline position errors are entirely eliminated.
[0016] In one practical embodiment, the means for generating a
digitized image of the cast shadow of the global axis of gravity
include:
[0017] a calculation unit and an associated memory,
[0018] geometrical data, stored in the memory, and corresponding to
the relative positions of the source of X-rays, the plane of the
sensitive plate, and the patient support means in a fixed system of
axes,
[0019] a program stored in a program memory area of the memory for
storing said position signals at the time of taking the
radiographic image, calculating, as a function of said position
signals, the straight line segment intersecting the plane of the
sensitive plate and the vertical plane passing through the source
of X-rays and the horizontal position of the global axis of
gravity, and storing the result of this calculation, which
constitutes the image of the global axis of gravity.
[0020] The system is preferably such that:
[0021] it includes a scanner for scanning the radiographic image
produced on the target plate sensitive to X-rays and producing a
series of digital signals constituting the digitized radiographic
image,
[0022] the program is adapted to receive said digital signals and
stores them in the memory,
[0023] the program is adapted to modify the stored digitized
radiographic image by substituting the image of the global axis of
gravity, thereby generating said combined digitized image,
[0024] and the program is adapted to display said combined
digitized image on a monitor or prints it out on a support.
[0025] In a preferred embodiment, further improving accuracy, the
program includes a calibration sequence, adapted for scanning the
radiographic image of a calibration object with radio-opaque
markers, and calculating said geometrical data from known positions
and dimensions of the radio-opaque markers of said calibration
object, and storing the data in the memory. This solves the problem
of uncertainty related to the unknown position of the source of
X-rays, which is generally incorporated into an X-ray head whose
interior cannot be seen. By positioning the calibration object
appropriately and in a marked way on the patient support means, and
taking a radiographic image of the calibration object when so
positioned, all the geometrical data necessary, i.e. the relative
positions of the source, the patient support means and the target
plate, is determined in one operation, enabling subsequent accurate
calculation of the position of the image of the global axis of
gravity relative to the radiographic image of the bones of the
patient.
[0026] One cause of the lack of accuracy and reliability of prior
art systems that include a force plate for detecting the horizontal
position of the global axis of gravity of the patient is the
possibility of drift in the specifications of the force plate
sensors. As a result of such drift, the signals produced by each of
the sensors can vary in time, which leads to an erroneous
determination of the position of the global axis of gravity. The
invention solves this problem by providing a calibration weight and
a calibration sequence to be effected periodically. The calibration
weight, which is removable and can be positioned on the patient
support means, has a particular shape, position marker means which
can be made to coincide with complementary marker means on the
patient support means, and a center of gravity whose position
relative to the position marker means is known. The calibration
sequence, provided in the stored program, is adapted to calculate
correction parameters for the force signals produced by each
sensor, so as to make the calculated center of gravity coincide
with the known geometrical position of the real center of gravity
of the calibration weight. The correction parameters are then
stored in memory for subsequent reliable calculation of the
position of the global axis of gravity of the patients.
[0027] To improve accuracy, the fixed system of axes preferably has
its center in the vertical plane passing through the source of
X-rays and perpendicular to the support means for the target plate
sensitive to X-rays.
[0028] The patient support means preferably include armrests on
which the patient can rest his arms in a defined advanced
position.
[0029] In one advantageous embodiment, the patient support means
are rotatable about a median vertical axis to orient the patient
angularly relative to the direction between the source of X-rays
and the support means for the target plate.
[0030] In one preferred embodiment, the armrests are attached to a
turntable which itself carries a modified weighing machine force
plate on a plurality of force sensors distributed at marked
positions relative to the system of axes and producing force
signals used as position signals by the calculation unit and the
program.
[0031] The system preferably includes means for indexing
selectively the angular position of the patient support means at
least every 45.degree..
BRIEF DESCRIPTION OF THE DRAWINGS
[0032] Other objects, features and advantages of the present
invention will emerge from the following description of particular
embodiments of the invention, which is given with reference to the
accompanying drawings, in which:
[0033] FIG. 1 shows diagrammatically and in perspective an
evaluation system conforming to one embodiment of the present
invention;
[0034] FIG. 2 is a front view in diametral section of patient
support means of the FIG. 1 evaluation system;
[0035] FIG. 3 is a plan view of the evaluation system from FIG.
1;
[0036] FIG. 4 is a perspective view showing the calibration step
using a calibration object; and
[0037] FIG. 5 is a simplified block diagram showing the essential
hardware and software for carrying out the calculations that
generate images in accordance with the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0038] In the embodiment of the system shown in FIGS. 1 and 3, the
system includes a source 1 of X-rays, support means for supporting
a target plate 2 sensitive to X-rays and oriented vertically at a
particular horizontal distance from the source 1 of X-rays, and
patient support means 3 adapted to support a patient 4 in a fixed
position between the source 1 of X-rays and the support means for
the target plate 2. The system according to the invention is an
installation for taking radiographic images. In other words, the
source 1 of X-rays, and the support means for the target plate 2
can have a structure like those habitually used in medical
radiographic image installations.
[0039] In accordance with the invention, the patient support means
3 include means for detecting the horizontal position of the global
axis of gravity 5 of the patient 4 (the vertical axis passing
through the center of gravity G of the patient), i.e. its
coordinates in the horizontal plane, during operation of the source
1 of X-rays.
[0040] A priori, the invention can be applied to analyzing the
equilibrium of patients 4 in diverse positions such as the standing
position or the seated position, for example. FIG. 1 shows an
embodiment of the system according to the invention in which the
patient support means 3, the source 1 of X-rays and the support
means for the target plate 2 produce a radiographic image and
simultaneously identify the global axis of gravity 5 of a standing
patient 4.
[0041] For analyzing the spinal column, the system is adapted to
take a radiographic image of the thoracic area, the lumbar area,
the pelvic area and the upper femoral area of the patient 4 in the
standing position.
[0042] In the embodiment in which the patient 4 is standing, it is
important for the arms 6 and 7 of the patient to have a constant
defined position, because their position affects that of the center
of gravity G and the quality of the radiographic image obtained.
For example, as shown in the figure, the patient supporting means 3
include armrests 8 and 9, for example vertical rods, on which the
patient 4 can rest his arms 6 and 7 in an advanced position, for
example in a horizontal position, gripping the rods 8 and 9 with
his hands.
[0043] The patient support means 3 are preferably rotatable about a
median vertical axis 10, enabling the patient 4 to be oriented
angularly relative to the direction of propagation of rays between
the source 1 of X-rays and the support means for the target plate
2, with several successive angular positions in which a plurality
of radiographic images can be taken, for example from the front and
then from the side. Indexing means selectively fix the angular
position of the patient support means 3 with respect to the median
vertical axis 10 in at least eight positions spaced by
45.degree..
[0044] In the advantageous embodiment shown in FIGS. 2 and 3, the
patient 4 rests on patient support means 3 including a modified
weighing machine force plate 15 which is provided with a plurality
of force sensors such as the sensors C1, C2 and C3, arranged in
positions that are marked relative to a system of axes XbObYb, and
associated with calculating means for calculating the position Og,
in the horizontal plane, of the resultant of the forces in said
system of axes XbObYb. More than three sensors can naturally be
provided.
[0045] The system of axes XbObYb can advantageously have its center
Ob in the vertical plane XOZ passing through the source 1 of X-rays
and perpendicular to the support means for a target plate 2
sensitive to X-rays.
[0046] For example, as shown from the front and in section in FIG.
2, the patient support means 3 include a fixed plate 12, which can
be fixed to the floor, on which is mounted a turntable 13
journalled on a top pivot 14 of the fixed plate 12. Thus the top
pivot 14 defines the rotation axis of the turntable 13, which is
also the median vertical axis 10 of the patient support means
3.
[0047] The turntable 13 carries a modified weighing machine force
plate 15, which constitutes the surface supporting the patient
during operation of the evaluation system according to the
invention. The modified weighing machine force plate 15 can be
disc-shaped, for example, as shown in FIG. 3.
[0048] The modified weighing machine force plate 15 is connected to
the turntable 13 by at least three force sensors C1, C2 and C3,
adapted to evaluate the vertical bearing force between the modified
weighing machine force plate 15 and the turntable 13. As shown in
FIG. 3, for example, the force sensors C1, C2 and C3 are
equidistantly spaced at 120.degree. from each other around the
center Ob.
[0049] Vertical forces F1, F2 and F3 act on the three sensors C1,
C2 and C3.
[0050] The barycenter of the locations of the sensors C1, C2 and C3
assigned the coefficients F1, F2 and F3 is the point O.sub.g at
which the global axis of gravity 5 of the patient intersects the
bearing plane. This point O.sub.g is determined by elementary
calculations from known coordinates of the positions of the sensors
C1, C2 and C3 and measured values of the forces F1, F2 and F3. The
calculation applies the equation:
F1.{right arrow over (ObC1)}+F2.{right arrow over (ObC2)}+F3.{right
arrow over (ObC3)}=(F1+F2+F3).{right arrow over (ObOg)}
[0051] The above calculation can be carried out by an appropriately
programmed microcontroller integrated into the modified weighing
machine force plate 15, or located somewhere else, as will be
evident to the person skilled in the art.
[0052] As shown in FIG. 1, a calculation unit 21 and an associated
memory are preferably provided, for example a microcomputer and the
usual peripheral devices, such as a keyboard 22 and a monitor 23.
The calculation unit 21 is electrically connected to the patient
support means 3 to receive position signals generated by the
patient support means 3 and to calculate the coordinates of the
point Og.
[0053] According to the invention, scanning means 20 are provided
for digitizing the radiographic image of the patient on the support
means for the target plate 2. A scanner 20 adapted to scan the
radiographic image produced on the target plate 2 sensitive to
X-rays can be used for this purpose, and to produce a series of
digital signals constituting the digitized radiographic image. In
accordance with the invention, calculation and image processing
means are further provided for superimposing the digitized image Hg
of the global axis of gravity 5 in the vertical plane of the plate
sensitive to X-rays on said digitized radiographic image of the
patient.
[0054] The calculation means are preferably associated with memory
means for storing coordinates of the position Og of the resultant
of the forces on the modified weighing machine force plate 15 at
the moment the radiographic image is taken. Accordingly, the
relative position of the radiographic image of the patient and the
image Hg of the global axis of gravity 5 correspond exactly,
allowing for the inherent enlargement that results from the
principle of radiography, at the relative position of the skeleton
of the patient 4 and the position of his global axis of gravity 5
in the defined attitude in which the radiographic image is
taken.
[0055] FIG. 5 is a more detailed diagram of the calculations and
image generation means.
[0056] It shows the calculation unit 21 such as the central
processor unit of a microcomputer or a microprocessor, associated
with its peripheral devices such as the keyboard 22 and the monitor
23. The position signals generated by the force sensors C1, C2 and
C3 are sent to the calculation unit 21 via an analog/digital
converter 30. The calculation unit 21 carries out the calculation
previously mentioned to deduce therefrom the coordinates of the
global axis of gravity 5 in the fixed horizontal system of axes
XbObYb i.e. the position of the point Og. These coordinates are
stored in a data memory area 25 of the memory 24, which is itself
connected to the calculation unit 21.
[0057] The data memory area 25 further contains other geometrical
data corresponding to the relative positions in the system of axes
XbObYb of the source 1 of X-rays, the plane of the sensitive plate
2, and the patient support means 3.
[0058] A program is stored in a program memory area 26 of the
memory 24. The program is adapted to store said position signals at
the time the radiographic image is taken, which time is
communicated to the calculation unit 21 via an input connected to
the radiographic image apparatus. The program calculates, as a
function of said position signals or coordinates of the point Og,
the straight line segment Hg intersecting the plane of the
sensitive plate 2 and the vertical plane passing through the source
1 of X-rays and the horizontal position Og of the global axis of
gravity 5. The calculation result is stored in the memory 24, and
this calculation result constitutes the image of the global axis of
gravity 5.
[0059] Simultaneously, or later, the scanner 20 scans the
radiographic image produced on the target plate 2 sensitive to
X-rays, and produces a series of digital signals constituting the
digitized radiographic image. The program sends these digital
signals to the calculation unit 21 where they are stored in the
memory 24.
[0060] The program is also adapted to modify the digitized
radiographic image stored in the memory 24 by substituting points
in the image corresponding to the image of the global axis of
gravity Hg, so as to generate a combined digitized image.
[0061] Finally, the program is adapted to display said combined
digitized image on the monitor 23 or prints it out on a support.
The combined digitized image including the digitized radiographic
image 23a and the image 23b of the global axis of gravity is
therefore shown diagrammatically on the monitor 23.
[0062] In practice, it is not rare for there to be some
displacement between the source 1 of X-rays and the target plate
support 2, or for the exact position of the source 1 of X-rays not
to be known accurately, as it is generally hidden inside an X-ray
head. It is then not possible to calculate accurately the exact
position of the image Hg of the global axis of gravity 5.
[0063] To solve this problem, calibration means described below can
be provided.
[0064] As shown in FIG. 4, the calibration is effected during a
calibration sequence in which a radiographic image of a calibration
object 40 with known dimensions and a particular structure and
placed in a marked and appropriate position on the patient support
means 3 is produced. The calibration object 40 is advantageously a
radiotransparent plastics material parallelepiped, with dimensions
of 180 mm.times.180 mm.times.300 mm, for example, with eight 3 mm
diameter radio-opaque lead balls implanted at the vertices. The
calibration object 40 carries markings on its bottom base which are
made to coincide graphically with corresponding markings on the
patient support means 3.
[0065] The calibration object is X-rayed under the same conditions
as the patient, as shown in FIG. 4, by placing a target plate 2 in
the same position as the radiographic image to be made
subsequently.
[0066] The radiographic image obtained is then digitized with the
scanner 20, and the program includes a sequence adapted to
recognize the round shapes constituting the images of the balls in
the calibration object 40. For example, for a parallelepiped having
balls at its eight vertices A, B, C, D, E, F, G and H, an image
abcd is obtained of the front face, and a smaller image efgh of the
rear face.
[0067] The three coordinates of the source 1 of X-rays relative to
the fixed system of axes XbObYb are unknown, as are the three
coordinates of the center of the calibration object 40 relative to
the fixed system of axes, and two angular parameters representing
the possible inclinations of the calibration object 40 relative to
the system of axes XbObYb. To these eight unknowns there correspond
the sixteen measured coordinates of the eight images abcd, efgh of
the balls. The program measures the coordinates of these points
abcdefgh on the digitized image. A digital technique that will be
evident to the person skilled in the art is used to solve the
system of sixteen equations in eight unknowns. The redundancy, due
to the greater number of equations than unknowns, is used to
improve the accuracy of the calculations. The program therefore
deduces geometrical data that is then stored in the data memory
area 25 of the memory 24.
[0068] In practice, it is not rare for the technical specifications
of the force sensors C1, C2 and C3, which are electronic sensors
generating electrical signals, to drift in time and produce force
signals whose processing can no longer reproduce the exact position
of the global axis of gravity of patients.
[0069] Accordingly, in the situation where the patient support
means include a patient support force platform carried by a
plurality of force sensors, the system can advantageously be
recalibrated periodically using a calibration weight and a
calibration sequence.
[0070] The calibration weight is a removable weight that can be
positioned on the patient support means 3. The calibration weight
has a particular shape, for example a parallelepiped-shape like the
calibration object 40, or a cylindrical shape, and has a center of
gravity whose geometrical position within the volume of the
calibration weight is known. The calibration weight includes
position marker means, for example on its lower face, which marker
means are made to coincide with complementary marker means on the
patient support means 3. Accordingly, the geometrical position of
the center of gravity of the calibration weight relative to the
patient support means 3, and therefore relative to the fixed system
of axes XbObYb, is known.
[0071] The program stored in the memory includes a calibration
sequence which calculates correction parameters for force signals
produced by the sensors C1, C2 and C3 in order to make the
calculated center of gravity coincide with the known geometrical
position of the real center of gravity of the calibration weight.
The correction parameters are then stored in memory, to enable
reliable subsequent calculation of the position of the global axis
of gravity of patients.
[0072] Clearly the system according to the invention provides a
better understanding of the sagittal equilibrium mechanism. The
risks of error are minimized because the system produces the
relative position of the global axis of gravity 5 and the human
skeleton automatically and accurately.
[0073] The embodiment of the invention for making radiographic
images in the standing position takes the lower limbs into account,
and provides an improved interpretation of defects in the curvature
of the spinal column.
[0074] Using the radiographic image combined with the image Hg of
the global axis of gravity 5, the practitioner can measure the
distance between the global axis of gravity 5 and the axis of the
heads of the femurs. He can also identify the centers of the heads
of the femurs to evaluate the anterior-posterior offset between the
global axis of gravity 5 and the heads of the femurs.
[0075] After an operator makes specific marks on the radiographic
image with the aid of an appropriately programmed computer, the
system can reconstruct a spinal and pelvic model for improved
characterization and evaluation of the curvatures of the various
sections of the spinal column.
[0076] The present invention is not limited to the embodiments
explicitly described, but includes variants and generalizations
thereof within the scope of the following claims.
* * * * *